The present invention is directed to a method of and an apparatus for forming a uniform blanket of fibers and the blanket formed by the method and apparatus which is initially tubular in configuration and may be slit longitudinally and unfolded to form a blanket having fibers predominately oriented perpendicular to the longitudinal axis of the blanket.
In the manufacture of fibrous blankets using a rotary fiberization process, fibers are produced by the extrusion of a thermoplastic material, including glass and polymeric materials such as polypropylene and polyester through a large number of holes in a peripheral, annular wall of a fiberizing disc or rotor. The disc is rotated at a high rate of speed about a vertical axis causing the thermoplastic material within the disc to be extruded through the holes of the disc to form continuous fibers. The continuous fibers are issued from the holes of the disc in a substantially horizontal direction. These continuous fibers are directed downwardly toward a horizontal collection surface beneath the fiberizing disc by a substantially continuous, downwardly directed air stream which encircles the fiberizing disc. The horizontal collection surface is normally a foraminous conveyor belt passing over a suction chamber which draws air through the conveyor belt to draw the fibers onto the upper surface of the conveyor belt where a blanket of the fibers is formed. One such process of fiberization is described in connection with the manufacture of glass fibers in U.S. Pat. No. 4,058,386, issued Nov. 15, 1977, to D. H. Faulkner et al, and entitled "Method and Apparatus for Eliminating External Hot Gas Attenuation in the Rotary Fiberization of Glass (hereinafter the "386 patent"). The disclosure of this patent is hereby incorporated herein in its entirety by reference.
Several problems have been experience in the formation of fibrous blankets from substantially continuous fibers by the above referenced process. As the continuous fibers are directed downwardly toward the horizontal collection surface, the fibers twist beneath the fiberizing disc into a loosely twisted rope of fibers. In addition, the loosely twisted rope of fibers tends to snake back and forth across the moving collection surface in an irregular fashion and this results in the nonuniform, non-directional collection of the continuous fibers on the collection surface.
Accordingly, the blanket formed by this process is not uniform in thickness or density and has thin spots and/or holes which are undesirable when using the blanket as insulation or air filtration media. The problem of non-uniformity is magnified when thin blankets about one thirty-second of an inch to one inch thick are produced for air filtration or similar uses. Such blankets must have a uniform thickness and density throughout to prevent the passage of dirt or other matter through the filtration media. In addition to the above, the edges of the blanket produced by this process are irregular and this results in edge loss or scrap due to the need to trim the irregular edges from the blanket.
The blankets formed by this process are sometimes further processed by passing the blanket through a chopper to produce short length fibers (e.g. fibers from 1/4 to 3 inches in length) for use in processes, such as, paper making, carding, air layering, etc. For these products, it is desired to have the short length fibers produced in the chopping operation uniform in length. With the twist imparted to the continuous fiber tow in the collection process and the irregular collection of the fibers on the collection surface to form the blanket, the orientation of the fibers in the blanket is not unidirectional. Accordingly, when the blanket is chopped to form short length fibers, the fibers vary in length and manufacturing tolerances for fiber length are difficult to maintain. Thus, it would be desirable to manufacture a blanket wherein the fibers are highly directional in their orientation to facilitate the formation of uniform length fibers in the chopping operation.